The identification and characterization of proteins is an essential part of understanding biological processes. At Emory University, large number of research projects focus on the identification of proteins, the characterization of protein post-translational modifications, and the study of protein-ligand interactions. A significant portion of this work is carried out by the Emory University Microchemical Facility (EMF). Among the services that this core facility provides is the sequencing of proteins and characterization of protein modifications. Currently, the facility uses Edman degradation for sequence determination. While this technology is powerful and accurate, it is limited in flexibility, throughput, and in the quantity of sample that must be provided. To improve the capabilities of the facility and to aid the research efforts of Emory Investigators, we request funds to purchase a triple-quadrupole mass spectrometer. The instrument requires five times less starting material for sequence determination than our best Edman sequencing instrument. Additionally, the instrument will be on line with our current capillary or microbore LC, allowing mass and/or sequence determinations from a series of proteolytic digestions. This will increase greatly the success, speed,, and characterization of samples. The instrument will also be used to study receptor-ligand mediated interactions. The instrument's flexibility, sensitivity, and accuracy will be of tremendous importance to the productivity of the research projects described. This is of particular significance as we approach the completion of the DNA sequence of many genomes, including the human genome. The ability to identify and characterize protein sequences is the next phase in our understanding of the human genome and its expressed proteome.